The present invention relates to disc brakes for vehicles, and in particular to a system and method for mounting, removing and retaining brake pads in disc brakes, such as air-operated disc brakes utilized on commercial vehicles.
Pneumatically-operated disc brakes have been undergoing development and deployment on commercial vehicles since at least the 1970's, and are beginning to replace drum-style brakes due to advantages in areas such as cooling, fade resistance and serviceability. German Patent Publication No. DE 40 32 886 A1, and in particular FIG. 1 of this document, discloses an example of such an air disc brake. In this design, a pneumatic diaphragm chamber (pneumatic actuator) is attached to a rear face of the disc brake caliper housing, and applies a brake actuation force through a linear actuator rod to a brake actuator lever within the caliper. The brake's actuator lever in turn transfers and multiplies the force applied by the actuator rod to one or more spindles, which force brake pads against a brake disc or rotor. The terms “brake disc,” “rotor” and “brake rotor” are used interchangeably herein.
In applications such as commercial vehicles, wheel rims have historically been sized to only provide adequate clearance for the drum-type brakes historically employed on such vehicles. Because the resulting space envelope between the wheel and its axle is limited, the outer radius of the brake caliper, brake pads and any brake pad retention devices must conform to the limited available radial space. Brake pads typically have been located and retained on one of the brake caliper or brake caliper carrier/mount using transverse suspension pins and/or using leaf spring-type metal strips disposed over the outer radius of the brake pads. Brake pads have also been retained by capturing the brake pads between the caliper mounting frame and the portion of the brake caliper which straddles the brake disk. As one of ordinary skill will recognize, the same brake pad support function may be provided by a brake caliper carrier/mount designed to support the brake pads or by a brake pad carrier which is separate from the caliper mounting structure. For convenience in this description, the terms caliper carrier, caliper mount and brake pad carrier may be interchanged without intending to limit the brake pad supporting structure to any specific brake pad and brake caliper carrying structure.
A problem with the previous brake pad retention approaches is their tendency to allow the brake pad to rotate about an axis parallel to the brake disc rotation axis during brake application. This in-place rotation is referred to as “pad kick,” a motion that can generate undesired brake application noise due to brake pad vibrations, increase fatigue damage to the typical over-pad leaf spring retainer, and increase wear and damage to the brake pad and/or brake caliper mounting structure. An illustration of pad kick is provided in FIG. 13. When a brake pad 101 is applied against a friction surface of a brake disk (not illustrated) which is rotating in direction DR, the brake disk's rotation induces motion and reaction forces between the brake pad 101 and its adjacent mount abutment surfaces (not illustrated). At the leading edge 102 of the brake pad the brake pad attempts to move upward in direction LU in response to the friction forces along the face of the brake pad (illustrated here by force arrows across the face of brake pad 101). At the trailing edge 103 of the brake pad, the brake pad attempts to move downward in direction TD. However, because the brake pad 101 is constrained by adjacent mount abutment surfaces, the overall motion of the brake pad is generally a rotation about an axis parallel to the brake disk rotation axis. This motion may be unilateral during the brake application, or may manifesting itself as a moderate-to-severe oscillation of the brake pad in its mount, significantly increasing wear of the abutting brake pad and mount surfaces.
The present invention addresses these and other problems by providing a brake pad mounting and retention arrangement and method of installation and removal which provides increased brake pad retention and guidance, decreased pad kick and vibrations, and decreased component wear and fatigue.
In one embodiment of the present invention the brake pad is pulled upward (i.e., radially outward) by a spring reaction bar and springs over each brake pad to bias the surface features at the lateral sides of the brake pad against the undersides (i.e., radially inner sides) of corresponding surface features of the mount structure carrying the brake caliper and/or brake pads.
In a preferred embodiment the mount structure's brake pad abutments (also known as “mount horns”) have a large wedge-shaped or gear tooth-shaped surface facing the adjacent lateral side of the brake pad, and the brake pad has a corresponding indentation. As the spring reaction bar and springs pull upward on the brake pad, the lower surface of the pad abutment's wedge-shaped surface and the corresponding upward-facing surface of the lateral side of the brake pad cooperate to provide a broad pad contact surface area. This biasing configuration substantially suppresses pad kick and vibrations during brake application.
Further preferably, the brake pad and mount structure are configured in a manner such as that shown in U.S. Pat. No. 8,540,061, in which the brake pad and the mount abutments cooperate to allow vertical insertion (i.e., in the radially inward direction) of the brake pad into the mount at a portion of the mount abutment farthest from the brake disc, followed by translation of the brake pad in the axial direction toward the brake disc to advance the lateral surface features of the brake pad and the mount abutment into engagement with one another.
The structure that pulls the installed brake pad upward may include a spring reaction bar that is configured to be removably fixed to the brake caliper, with one or more spring that are supported on the spring reaction bar and engaging features on the upper (i.e., radially outer) surface of the brake pad backing plate to bias the brake pad upwards.
In one embodiment, the spring reaction bar may be a bar with a first end that is received by the brake caliper, such as by sliding into a corresponding slot at or near the opening in the brake caliper through which the brake pads may be inserted or removed without removal of the brake caliper from its mount. The second end of the spring reaction bar may be configured to be captured at the opposite side of the pad insertion opening, for example, by having a slot through which a tab of the brake caliper can protrude to receive a retaining pin. The spring reaction bar may also be configured with portions of multiple radial heights, for example a radially high center portion to provide additional clearance between the bar and the outer radius of the brake disc, and radially lower side portions that are configured to be located in corresponding lateral guidance grooves at the upper surface of the brake pad backing plate.
The springs that cooperate with the spring reaction bar may be leaf springs that are positioned above (radially outward of) the spring reaction bar and provided with lateral spring ends that positively engage corresponding spring-receiving features at the upper surface of the brake pad backing plate and draw the brake pad upwards to bias the wedge-shaped surfaces of the brake pad and the pad abutments against one another. Preferably the springs are preformed such that they may be pressed downward (radially inward) onto the upper surface of the brake pad backing plate and elastically deform to cause the tips of the springs to slide along the top surface of the brake pad backing plate and into receiving slots of the brake pad backing plate. In this embodiment, the tips of the leaf springs are formed in an S-shape, with the height of the S-shape being such that the tips are held by friction in the backing plate receiving slots.
A further embodiment of the present invention includes additional elements that may be inserted between the radially outer surface of the spring retaining bar and the radially inner surfaces of the leaf springs to increase the biasing forces applied in the radially outward direction by the leaf springs to their brake pads.
As an alternative to forming the tips of the leaf springs in an S-shape, the tips of the leaf springs may be provided with features such as a hole configured to engage corresponding features such as hooks on the brake pad backing plate to ensure positive engagement between the springs and the brake pad.
Other brake pad backing plate and spring arrangements are possible within the scope of the present invention, such as springs mounted to the underside of the spring retaining bar, use of more than one spring retaining bar cooperating with one or more spring segments, or spring tips with different shapes, as long as the structure biases the brake pad upward against the laterally-projecting mount horn pad abutment features.
A method of assembly of an embodiment of the present invention includes withdrawing the brake caliper actuator (for example, brake application spindles) a sufficient distance to allow insertion of the brake pads, vertically (i.e., in the radially inward direction) inserting a brake pad through the brake caliper's brake pad insertion opening until the lateral surface features of the brake pad are aligned with the corresponding mount horn abutment features, advancing the brake pad toward the brake disc to engage the corresponding lateral surface features, installing the spring reaction bar across the brake pad insertion opening, placing the spring over the spring retaining bar and pressing downward (radially inward) on the spring until the lateral tips of the spring engage the spring receiving slots on the upper surface of the brake pad backing plate. Removal of the brake pads may be accomplished by reversing the installation method, either with or without tools as necessary to disengage the spring tips from the brake pad backing plate.
Another embodiment of the method would include placing the brake pads in the mount prior to locating the brake caliper on its mount. The remaining component installation would be similar to the above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.